In recent years, Global Navigation Satellite System (GNSS) satellites are utilized to provide user terminals with data regarding their respective locations. Global Positioning System (GPS) is one of the more recognized examples of a GNSS that consists of a network of satellites. GNSS satellites broadcast their own ephemeris information and clock corrections, as well as the almanac for the entire constellation of satellites. The almanac is a reduced set of the ephemeris parameters that can be generated from ephemeris information, at a reduced resolution and accuracy. Both the ephemeris data and the almanac data transmitted by the GNSS satellites are in Keplerian coordinates. However, due to slow data transfers from GPS satellites to the user terminals, the transmission of such information to the user terminals directly from the GPS satellites can take up a substantial amount of time (e.g., up to 55 seconds for valid almanac data, up to 15 minutes with no information, etc.). A prolonged first fix time, which is the period required for a GPS receiver to acquire satellite signals and navigation data and to calculate a position solution, can negatively impact associated applications, and thus, user experience. Without having the ephemeris or almanac information, a user terminal will not be able to quickly determine which of the GPS satellites from the constellation are visible at any time, and thereby, must perform an exhaustive search. Receiving a separate faster broadcast from an alternative source, for example a communications system, containing the ephemeris and almanac reduces time and power consumption by the user terminal. If the Keplerian coordinates are compressed into a format which contains fewer bits then the time to first fix can be improved further while reducing the overhead imposed on the communications system.
The ephemeris broadcast by the GPS satellites is in the format of Keplerian parameters. To reduce the time of Time To First Fix (TTFF), in a terrestrial wireless system (e.g., a 3GPP system), the ephemeris information is rebroadcast to the user terminals in the original format. In a mobile satellite system, such as Geo-Mobile Radio-1 Third Generation (GMR-1 3G), for the purpose of saving spectrum, the ephemeris of GPS satellites is preprocessed at the satellite base station subsystem (SBSS) and broadcast to the remote terminals in a much more compressed format of Earth centered Earth fixed (ECEF) coordinates. For a wireless terminal that can be used in both terrestrial and satellite systems, a function interface and approach is needed for the conversion between the ephemeris in Keplerian and ECEF formats, so that the terminal can perform TTFF in both systems.